Method of forming uranium carbide



Patented Dec. 25, 1951 UNITD STATES METHOD OF FORMING URANIUM CARBIDE NoDrawing. Application February 3, 1947, Serial No. 726,225

3 Claims. 1

This invention relates to uranium-carbon compounds and more particularlyto uranium-carbon alloys having a low carbon content. More specifically,the invention is concerned with the formation of uranium monocarbide.

Broadly stated, it is well-known in the art that when uranium and carbonare heated in contact with each other at an elevated temeprature for asufiicient period of time, a compound or alloy may be formed having auranium-carbon composition. The structural composition of the alloy orcompound thus formed is dependent upon the stoichiometric amounts ofcarbon and uranium present and upon the temperature at which thealloying occurs.

When the uranium-carbon alloy is heated to a temperature in excess of2300" C., approaching 2400 0., there is formed an alloy, uraniumsesquicarbide (U203) which will disproportionate upon cooling to uraniumdicarbide (U02). The art does not reveal the existence of any othercharacteristic alloy of the uranium-carbon system, other than uraniumdicarbide and uranium sesquicarbide.

In accordance with a specific embodiment of this invention, it is hereincontemplated to form uranium monocarbide (UC) in distinct proportionsfrom uranium dicarbide (U02) and uranium sesquicarbide (UzCs) Otherobjects and advantages of this invention will be readily apparent fromthe following description of the preferred embodiments of thisinvention.

It has been found in accordance with the method of this invention thatspecific uranium compounds or alloys containing carbon may be preparedby heating uranium metal in contact with methane at an elevatedtemperature.

The solubility of carbon in comminuted uranium metal is extremely lowwhen the uranium is in the beta state having a temperature between 660and 770 C. The solubility of the carbon in the beta-uranium is of theorder of approximately 0.03% (0.6 atom percent) C. while in theuranium-alpha phase, less than 660 0., the solubility is of the order of0.01% (0.2 atom percent) C. As the temperature of the uranium metal isincreased, the solubility of the carbon approaches a maximum in theliquid uranium phase, greater than 1125 C. It shall be noted that carbonis slightly soluble in uranium metal when the uranium metal is in thealpha phase, and that a slight solubility of carbon even occurs when theuranium metal is heated at a temperature of about 400 C.

In examinin the existence of uranium-carbon alloys over a temperaturerange from about 400 C. to a temperature in excess of about 2375 0.,there is evidence for the existence of a high temperature uranium-carbonalloy having the structural formula of U203. Upon cooling, this compound(U203) disproportionates into uranium-carbon compounds, primarily UCz.In order to form uranium-carbon compounds having at least two atoms ofcarbon per one atom of uranium, it is found that the carbon content mustexceed 4.8% by weight and that the temperature must be in excess of themeltin point of the uranium metal at about 1125 C. In addition, it isfound that by increasing the temperature to about 1800 C., a greaterproportion of uranium dicarbide is formed.

In examining the carbon-uranium system, the proportion of carbon touranium must exceed 4.8% by weight to form the dicarbide and less than4.8% carbon to form the uranium monocarbide.

Uranium-carbon alloys may be prepared by contacting a hydrocarbon gas,such as methane, with comminuted' uranium metal and allowing the methanegas to be in continuous contact with the uranium in an amountproportional to a stoichiometric amount to form the desireduranium-carbon alloy. In addition, it is noted that after forming theuranium-carbon alloys, primarily uranium dicarbide at an elevatedtemperature, the alloy ma be quenched to a temperature less than themelting point of the uranium metal, less than 1125 C., so thaturanium-carbon alloy thus formed disproportionates into another specificuranium-carbon alloy, primarily uranium monocarbide. The uranium-carbonalloy produced by quenching exhibited a dendritic structure identifying.a preponderance of uranium monocarbide. The uranium monocarbide thusproduced did not exhibit an extremely high purity, since a smallpercentage of uranium dicarbide was still present; another method forproducing uranium monocarbide was therefore devised.

In accordance with another embodiment of the invention uraniummonocarbide of high purity may be prepared by reacting a hydrocarbon,such as methane, in contact with uranium metal at a temperature lessthan the meltin point of the uranium metal. In this mode of preparationthe tendency toward the formation of uranium-carbon alloys other thanuranium monocarbide is considerably reduced. In addition, by introducingthe carbon content, by means of methane, and the uranium content instoichiometric relationships, the tendency to specifically form uraniummonocarbide is increased.

As an example, uranium monocarbide may be formed by contactingcomminuted uranium metal of high purity in an enclosed vessel withhydrocarbon gas, such as methane, of high purity, and then increasingthe reaction temperature to a temperature in excess of about 400 C. Thereaction talges place as shown in the following formula;

The preferred mode of operation embodies the use of a continuous flowsystem wherein purified methane is allowed to flow and contact a heatedcomminuted uranium mass in a stoichiometric amount wherein the amount ofcarbon supplied by the methane gas shall not be in excess ofapproximately 4.8% by weight. The operating temperature for forming theuranium monocarbide, in this particular process; is considered to bebetween 400 and the melting point of uranium which is about 1125 CJ;although the preferred u 2UH3 heat The uranium metal then reduces themethane and combines with the carbon of the methane, and this may beillustrated by the following equation:

U on Q. 2UC 211,, 400 o.

The combined reaction may be illustrated in the followin manner:

The reaction shown in Equation 3 is consideredto be exothermic; andalthough the initial decomposition temperature may be approximately 435C. there will be a rise, in temperature pro-. portional to the heat ofreaction.

It has been found that a relatively high proportion of uraniummonocarbide is formed when the amount of reactants is held to therequired stoichiometric proprotions relative to the amounts required toform uranium monocarbide and when the temperature of the reaction ismaintained at about 900 C.

It shall be also noted that uranium carbon alloys may be formed by usingthis. process wherein the stoichiometric amount of carbon exceeds the4.8% relationship to the uranium content and when the temperatureexceeds the melting point of the uranium metal. It has been found thatin using this mode of reaction the uranium carbon alloys having anatomic carbon content greater than one will disproportionate uponcooling or quenching to form uranium monocarbide. This method does notproduce relatively pure uranium monocarbide. but produces a mixture ofdendrites including uranium monocarbide and uranium dicarbide.

Thus, I have been. able. by following. the process described and claimedherein to consistently produce a mass of uranium monocarbide havin apredetermined carbon content proportional to the stoichiometric amountrequired to form the uranium monocarbide.

While the foregoing embodiments of the invention have been discussed asperformed at atmospheric pressure in a dynamic system involving thecontinuous flow of methane through the reactive mass of uranium oruranium hydride, a batch process has also been found suitable whereinstoichiometric amounts of uranium and carbon have been introduced intothe system and the reaction carried out in a similar manner. Althoughmethane is preferred, particularly for obtaining uranium monocarbide, itshall be noted that the, invention shall not be limited to methane andthat other compounds may be used to introduce the carbon content; suchcompounds may be ethane, propane, and other similar hydrocarboncompounds.

Numerous variations and modifications in the preferred methods andexamples described will be readily apparent and may be made withoutdeparting from the spirit and scope of the invention as defined in thefollowing claims.

The composition, uranium monocarbide, and a process of manufacturing itby the reduction of uranium oxide with carbon, are the subject matter ofthe Patent No. 2,448,479 granted to Harley A. Wilhelm and Adrian H.Daane on August 31, 1948.

What is claimed is:

1 A process for producing uranium monocarbide which comprises heatinuranium metal in contactwith methane in stoichiometric amounts at atemperature about 400 C. and less than 1125 C. wherein the carboncontent thus introduced is equal to about 4.8% to the uranium metalcontent.

2. A method of preparing uranium monocarbide, comprising heatingstoichiometric quantities of uranium with methane at substantially 900C.

3. A process. for producing uranium monocarbide, which comprises heatinguranium metal in contact with a quantity of aliphatic hydrocarboncorresponding to about 4.8% carbon with regard to the uranium metal at atemperature above 400 C. and less than 1125" C.

' RAY WM. FISHER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 560,291 Acheson g May 19, 18962,380,008 Abrams et a1. July 10, 1945 OTHER REFERENCES Friend, Textbookof Inorganic Chemistry, vol. VII, Part III, pages 333-334 (1926), pub.by Charles. Grifiin and Co., London; copy in Sci. Lib.

Fuels and Their Combustion by Haslam et al,. McGraw-Hill Book Co., Inc.(1926), p. 185. (Copy in Division 59.)

Mellor, Inorganic and Theoretical Chemistry, vol. XII, pp. 10 and 32(1932), Longmans, Green and Co., London.

Hansen, Aufbau der Zweistofflegierungen, p. 384 (1943), Edwards Bros,Ann Arbor, Mich. (Copyin Division 3.):

1. A PROCESS FOR PRODUCING URANIUM MONOCARBIDE WHICH COMPRISES HEATINGURANIUM METAL IN CONTACT WITH METHANE IN STOICHIOMETRIC AMOUNTS AT ATEMPERATURE ABOUT 400* C. AND LESS THAN 11250 C. WHEREIN THE CARBONCONTENT THUS INTRODUCED IS EQUAL TO ABOUT 4.8% TO THE URANIUM METALCONTENT.